The use of traffic control devices to provide a means for a safe and orderly flow of vehicle traffic have been known for over 200 years. The first known traffic control device for regulating street traffic was installed in 1868 in London, England at the intersection of George and Bridge Streets near the Houses of Parliament. This first traffic control device was designed by railroad signal engineer JP Knight. His device had two semaphore arms which, when extended horizontally, meant “stop”; and when drooped at a 45-degree angle, meant “caution.” At night, red and green gas lights accompanied the “stop” and “caution” positions. Since this early example of a traffic “stop light”, there have been numerous inventions directed towards various apparatus and systems for controlling traffic.
During the time since JP Knight's first invention, vehicle travel upon the roadways has increased dramatically thereby necessitating the need for more “intelligent” traffic control devices.
To this end, electronic traffic control systems were eventually developed and employed to regulate traffic at intersections. Some of the earliest examples of such systems were comprised of a single unitary stop light structure that was hung directly in the center of an intersection with appropriate colored lights projected to each direction where traffic was to be controlled. This single stop light was hard wired to communicate with a separate control box positioned in a safe area away from traffic, such as on the ground adjacent to the intersection. This type of control box controlled traffic flow by utilizing a hard wired circuit comprised of multiple analog timers and a compliment of solenoids. Systems such as this merely executed an established algorithm and did not vary “stop” and “go” patterns. In other words, once this traffic control system was configured, it did not have the ability to discern if an outside condition was present that would require altering its pre-configured traffic control patterns.
As technology progressed and traffic control systems became more sophisticated, the older control boxes were replaced with modern digital processors. These digital processors gave traffic control systems the ability to sense and process the detection of approaching vehicles in order to provide the traffic control system with some flexibility to alter preconfigured traffic pattern algorithms based upon data inputted from external sensors. Such early input sensors were limited to inductive loops embedded within the roadway surface. Inductive loop sensors have always been expensive to install and maintain, and in fact provided only a limited amount of useful data to the traffic control system. Furthermore, inductive loop sensors are often unreliable and require a great deal of calibration once embedded within a roadway surface. After installation the configuration time for these sensors is significant since the inductive loops must be manually tuned and physically wired into the traffic controller in the proper configuration. Thus, detection zones established by inductive loop sensors must be predetermined by physically embedding said loop sensors within the roadway surface at predetermined locations. The inductive loop sensor must be physically wired to the traffic controller in order to provide input to said traffic controller. High installation costs are attributed at least in part due to the need to install loop sensors for each and every approach to an intersection where vehicle traffic monitoring is desired. Typically, embedded inductive loops are limited to providing the traffic control system with simple data such as whether or not a vehicle is present upon the roadway somewhere within the monitored area where an inductive loop has been installed. Of course the monitored zones defined by inductive loop sensors cannot be easily changed as the roadway itself must be altered with sizable grooves to accept the inductive loop sensors. Such loop sensors are still in use today upon roadways around the world.
As roadway traffic continued to increase new traffic control systems were needed which possessed the ability to adapt to real-time traffic conditions and patterns based upon changing events upon the roadway, various times of day, or days of the week.
To this end, modern sophisticated traffic control systems were developed which implement one or more video cameras or microwave transceivers configured to provide input data to the traffic control system. This inputted data from external sensors assists the traffic control system in properly actuating traffic control devices in response to the detection or lack of detection of vehicles within various user defined portions (zones) of the roadway. For example, external sensors can enable a traffic control system to skip unnecessary signal phases such as a left turn lane when no vehicles are detected in that particular zone. External traffic sensors can also enable a traffic signal to increase green light duration for major arterials by presenting a green light in the lesser traveled cross streets (and thus a red light for a major arterial) only when vehicles are detected upon the lesser travel cross street. Thus, external traffic sensors assist in properly actuating a signalized intersection to improve traffic flow.
External traffic sensors can be utilized to assist in controlling traffic at any intersection or convergent point where vehicle movement is detected upon a surface. Examples of vehicles for purposes of this specification include but are not limited to, automobiles, trucks, motorcycles, water going vessels, pedestrians on foot, pedestrians operating mobile apparatus, aircraft and trains. In this specification and in the following claims, the term intersection means any point of convergence by two or more thoroughfares carrying vehicles.
Video detectors have been deployed as external sensors at intersections to alert the traffic control system when vehicles are approaching the intersection. To this end, a video camera is placed high above the intersection on a dedicated mounting arm such that the video camera's view covers one approach to the intersection. The video signal from the camera is digitally processed to create detection indicators when a vehicle is located within a user configured zone. Since a dedicated mounting arm is often necessary and one camera per approach is required, the installation cost of a video detector system can be expensive and time consuming. Furthermore, a time consuming process is usually required to configure video sensors for operation. Since video detectors rely upon visually detecting movement upon the roadway, they are affected by any environmental event which limits visibility such as darkness, rain, snow, fog, or when the sun is positioned in a manner which causes a glare upon the roadway or images to be detected by the video detector. For this reason, data produced by video detectors is often inconsistent or unreliable.
Microwave sensors have also been employed as external sensors to gather traffic related data for traffic control systems. Unlike video sensors, microwave sensors are not affected by weather events. Microwave sensors typically do not require a dedicated mounting arm since they are usually mounted much lower in relation to the ground than a video detector. Most microwave sensors also have the capability to monitor a wider geographic area than a video detector.
Although microwave and video sensors are able to provide much more useful information that inductive loops, neither sensor is one hundred percent reliable when detecting and maintaining the position of a vehicle from the time it enters a monitored detection zone until such time it exits the monitored detection zone. Failing to track a vehicle from the time it enters a monitored detection zone until such time as it exits the monitored detection zone is called occlusion. Although microwave and video sensors do overcome some of the disadvantages presented by inductive loop sensors, both are prone to occluding vehicles from detection when certain conditions are present.
Speaking to microwave sensors in particular, occlusion may occur anytime the view of the approaching vehicle is obstructed (even momentarily) from the sensor. Such obstructions can occur as a result from roadway conditions or when other traffic obscures or hides a previously detected vehicle from the outputted signal of the microwave sensor.
When an occlusion occurs, a vehicle may nevertheless be present upon the monitored portion to the intersection even though it is no longer being detected by the sensor. When this occurs the vehicle would be forced to wait longer for a green light until such later time as the microwave sensor regains detection of the vehicle, or until the next timed traffic cycle provides a green light. It would therefore be useful if a traffic control system was configured to minimize the number of occlusions.
Accordingly, the present invention overcomes the aforementioned shortcomings of the known prior art and provides improvements to the above stated shortcomings. The present invention is summarized and described in detail below.